Project Summary 1. IKKalpha in skin cancer development. Ultraviolet B light (UVB) is a common cause of human skin cancer. UVB irradiation induces mutations in the tumor suppressor p53 gene and chronic inflammation, which are essential for UVB carcinogenesis. IKKalpha plays an important role in maintaining skin homeostasis. Expression of IKKalpha was found to be downregulated in human and murine skin squamous cell carcinomas. However, the role of IKKalpha in UVB skin carcinogenesis has not been investigated. Thus, here we performed UVB carcinogenesis experiments on Ikkalpha+/+ and Ikkalpha+/- mice. Ikkalpha+/- mice were found to develop 2 times more skin tumors than did Ikkalpha+/+ mice following chronic UVB irradiation. The tumor latency was significantly shorter and tumors were bigger in Ikkalpha+/- than in Ikkalpha+/+ mice. At the early stage of carcinogenesis, the increase in UVB-induced p53 mutations, macrophage recruitment and mitogenic activity, and the decrease in UVB-induced apoptosis were detected in Ikkalpha+/- compared with those in Ikkalpha+/+ skin. Also, reduction of IKKalpha in keratinocytes up-regulated the expression of monocyte chemoattractant protein-1 (MCP-1/CCL2), TNFalpha, IL-1 and IL-6, and elevated macrophage migration, which might promote macrophage recruitment and inflammation. Therefore, these findings suggest that reduction of IKKalpha expression orchestrates UVB carcinogen, accelerating tumorigenesis. 2. IKKalpha in lung cancer development. IKKalpha downregulation has been reported in human squamous cell carcinomas (SCCs) of the skin, lungs, and other organs. Although we have previously demonstrated that IKKalpha deficiency promotes or induces skin SCCs in mice, we did not have evidence for the role of IKKalpha in lung SCCs in mice. Our recent results showed that approximately 30% of Ikkalpha-KA/KA mice expressing a kinase-dead and reduced IKKalpha develop lung SCCs. Because most Ikkalpha-KA/KA mice develop severe skin lesions (wounds and inflammation) and some develop skin tumors, these mice start to die after 6 months of age. To reduce the skin phenotypes in the mice, we introduced two types of transgenic IKKalpha into the epidermis of Ikkalpha-KA/KA mice. After the Lori.IKKalpha transgene, which is only expressed in the epidermis, was introduced into Ikkalpha-KA/KA mice, the skin conditions were greatly improved and Ikkalpha-KA/KA/Lori.IKKalpha mice were able to live longer. Almost all the Ikkalpha-KA/KA/Lori.IKKalpha mice develop lethal SCCs. Because SCCs are derived from lung epithelial cells expressing keratin 5 (K5), we then introduced the K5.IKKalpha gene into the skin and lungs in Ikkalpha-KA/KA mice. Most Ikkalpha-KA/KA/K5.IKKalpha mice can even live much longer than Ikkalpha-KA/KA/Lori.IKKalpha mice. No SCCs have been found in Ikkalpha-KA/KA/K5.IKKalpha mice but a few (&lt;10%) of the mice developed alveolar carcinomas. These preliminary results indicate that IKKalpha deficiency is involved in lung SCC development and that IKKalpha is capable of preventing SCC development in lung epithelial cells.